﻿98 ON THE CLASSIFICATION OF BIRDS. 



graduated. Many of our own little warblers, whose 

 flight is evidently feeble, and whose wings are almost 

 rounded, leave us in autumn, and only return in the 

 spring ; so that probably the very same journey is per- 

 formed by birds of the most opposite qualities of flight. 

 The ducks, which go to and from the northern regions 

 at stated periods, afford us another instance of very short 

 winged birds habitually migrating to great distances. It 

 is obvious, nevertheless, that the degree of speed with 

 which these several species proceed must entirely depend 

 upon the formation of their wings. 



(88.) The tail of a bird is formed to act in unison 

 with its wings, in performing the function of flight, 

 during which it is expanded, and it is used as a rudder. 

 There are very few birds without this member, although 

 in many it is very short. It is longest in the Rasorial 

 types, and shortest in the Natatorial and Grallatorial : in 

 the birds of this latter division, however, its office, in a 

 great measure, would seem to be performed by the legs, 

 which are extended backwards during flight, in the 

 direction of the tail. We can scarcely suppose, indeed, 

 that the flight of the heron would be so steady and 

 graceful, was the course of the bird simply directed by 

 a tail which hardly exceeds three inches in length. It 

 must not be supposed, however, that the degree of speed 

 with which a bird flies is to be estimated by the de- 

 velopment of this member ; for it generally happens that 

 birds with very large tails have proportionably short 

 wings. The peacocks and turkeys are familiar instances 

 of this relative disproportion, and the same may be 

 traced through a large proportion of those birds by which 

 they are represented in other groups. Hence it is evi- 

 dent that the structure of the tail is in some birds more 

 adapted for ornament than for flight. We shall now 

 enumerate the different forms it assumes, and the espe- 

 cial offices, where known, which these forms are intend- 

 ed to perform. In speaking of the comparative length 

 of this member we call that a short tail which, at the 

 most, does not exceed half the length of the wings ; a 



